完形填空（共20小题；每小题1.5分，满分30分）阅读下面短文，掌握其大意，然后从1—20题各题所给的四个选项（A、B、C和D）中，选出可以填入空白处的最佳选项。
Throughout history man has had to accept the fact that all living things must die. But people now live longer than they 1 . Yet, all living things still show the 2 of aging, which will eventually 3 death.
Aging is not a disease, but as a person passes maturity (成熟期), the cells of the body and the 4 they form do not function as well as they 5 in childhood and teenage years. The body provides less 6 against disease and is more 7 to have accident.
A number of related causes may 8 aging. Some cells of the body have a fairly long life, but they are not 9 when they die. As a person ages, 10 of brain cells and muscle cells decreases. 11 body cells die and are replaced by new cells. In an aging person the 12 cells may not be as workable or as capable 13 growth as those of a young person.
Another 14 in aging may be changes within the cells 15 . Some of the protein chemicals in cells are known 16 with age and become less elastic (有弹性的). This is why the skin of old people wrinkles (皱纹) and 17 . This is also the reason why old people 18 in height. There may be other more important chemical changes in the cells. Some complex cell chemicals, such as DNA and RNA, store and 19 information that the cells need． Aging may affect this 20 and change the information-carrying molecules so that they do not transmit the information as well.
1. A．would B．be used to C．used to D． used
2. A．function B．effect C．affect D． sign
3. A．lead in B．give in C．run into D． result in
4. A．hands B．feet C．heart D． organs
5. A．do B．has done C．did D． had done
6. A．energy B．protection C．vigor D． power
7. A．likely B．probable C．possible D． alike
8. A．attend to B．contribute to C．add to D． devote to
9. A．replaced B．reborn C．recovered D． surrendered
10. A．a number B．the amount C．the number D． a great deal
11. A．The others B．The other C．Another D． Other
12. A．old B．left C．new D． other
13. A．to B．for C．of D． in
14. A．factor B．effect C．reason D． element
15. A．for themselves B．of themselves C．themselves D． on their own
16. A．change B．to have changed C．to change D． to be changed
17. A．hangs loose B．hangs loosely C．is hanging loosely D． is hanging loose
18. A．increase B．shrink C．lengthen D． decrease
19. A．pass away B．pass by C．pass off D． pass on
20. A．improvement B．procession C．approach D． process